Central Costa Rica deformed belt: Kinematics of diffuse faulting across the western Panama block

Fault kinematics, seismicity, and geodetic data across central Costa Rica r eveal a diffuse fault zone, here named the Central Costa Rica Deformed Belt (CCRDB). The CCRDB defines the western margin of the Panama block and link s the North Panama Deformed Belt (NPDB) along the Caribbean coast with the Middle America Trench (MAT) along the Pacific coast. The junction of the CC RDB and the MAT coincides with an abrupt transition from smooth to rough cr ust on the subducting Cocos plate (rough-smooth boundary). Shallow subducti on of rough, thickened oceanic crust associated with the Cocos Ridge shifts active shortening into the volcanic are along faults of the CCRDB. Variabl e fault kinematics along this zone may reflect three combined deformation m echanisms: horizontal shortening and shear from oceanic ridge indentation, basal traction from shallow subduction, and localized block uplift from sub ducting seamount roughness. Within the forearc (domain 1), mesoscale faults express transtension where steep NE striking regional-scale faults interse ct the Pacific coast. Across the volcanic are (domain 2), mesoscale faults exhibit mostly sinistral and dextral slip on NE and NW striking conjugate f aults, respectively. Approaching the NPDB in the back are (domain 3), trans current faulting is modified by transpression and crustal thickening. Fault kinematics are consistent with earthquake focal mechanisms and Global Posi tioning System (GPS) measurements. Radiometric age constraints confirm that faulting postdates the late Neogene onset of shallow subduction. The ensui ng deformation front has propagated northward into the volcanic are to its present position along the seismically active CCRDB. Within the forearc, th e effect of shallow subduction is overprinted by local uplift related to un derthrusting seamounts.